<?php
add_action('wp_head', 'filter_category');
function filter_category(){?>
<script type="text/javascript">
    jQuery(document).ready(function($) {
        $('input[name="filter"]').click(function(){
           var searchIDs = $('input[name="filter-category"]:checked').map(function(){
                return this.value;
            }).toArray();
            alert(searchIDs);
        });
    });
</script>
<?php }
?>
